Various types of semiconductor integrated circuits (hereinafter abbreviated as “IC”), such as a battery monitoring IC for monitoring a battery, are mounted on a vehicle. The battery monitoring IC monitors each voltage of a plurality of battery cells connected in series. The battery monitoring IC prevents overcharge and/or over-discharge, and estimates quantity of a remaining battery. The battery monitoring IC includes a main power regulator and a sub power regulator. In a standby mode, the main power regulator is turned off, while the sub power regulator is kept operating to maintain such a condition that commands from an MCU are receivable by a communication control circuit.
An IC system having a standby mode reduces current consumption by the IC, thereby decreasing the overall power consumption. Examples of this type of IC system known in the art include a bias circuit directed at reducing power consumption, and a charge pump circuit achieving both reduction of charge-up time and reduction of power consumption. A further example known in the art is a battery save circuit capable of applying a battery power voltage Vcc to a band gap reference type voltage generating circuit in response to external signals without producing any voltage loss.
However, to allow cancellation of the standby mode, the power needs to be constantly supplied to a receiving circuit of the communication control circuit even in the standby mode. Therefore, current consumption in the standby mode is difficult to be reduced to 0 μA.